Recent research and development efforts in the field of next generation wireless communication systems aim at providing much higher data rates than existing systems. Generally, reference signals or pilot symbols which are usually in higher data rate wireless communication devices and systems, for performing initial time and frequency synchronization, cell identification, and channel estimation. Channel estimation indicates a process of compensating for distortion of a signal, which occurs by a rapid environment variation due to fading and restoring the transmission signal. For orthogonal frequency division multiplexing (OFDM) system, particularly, a reference signal or pilot symbol referring to a predetermined signal sequence is inserted at a predetermined location in time domain or frequency domain of a data stream, and communication devices is capable of detecting the reference signal or pilot symbol after receiving the data stream, and further performing time and frequency synchronization to measure channel information, and perform interference mitigation or cancellation.
A multiple-input multiple-output (MIMO) antenna technology using multiple transmission antennas and multiple reception antennas is also applied to improve data transmission/reception efficiency. In the MIMO system, a signal experiences a channel corresponding to each antenna. More antennas require more reference signals or pilot symbols, but pilot over-location occupies more channels and reduce amount of channel for transmitting data. Severe pilot overhead occurs, a transfer rate is decreased. Accordingly, it is necessary to arrange the pilots in consideration of multiple antennas.
In prior art, different pilot allocation structures have been designed and used, for example, in IEEE (Institute of Electrical and Electronics Engineering) 802.16e system the pilots are separated from each other in time domain, However, Although several design considerations for pilot structures have been discussed, currently there lacks a systematic approach to design pilot structures or patterns used in a multiple-input-multiple-output (MIMO) antenna system using orthogonal frequency division multiplexing (OFDM) modulation.